Insulating arrangement for optical insulation of integrated components and the method of manufacture

ABSTRACT

An isolating arrangement for isolating a portion of a substrate from the remaining portions of the substrate, characterized by the arrangement comprising a pair of obliquely extending slots which merge with each other in the interior of the substrate to isolate a portion or region of the substrate from the remaining portion, except at least one end of the portion extending between the slots. The slots are preferably formed by a laser-induced, wet-chemical etching and, subsequent to forming the slots, they can be filled with a material, such as metal or a ternary absorber material, to increase the isolation of the substrate region or portion.

BACKGROUND OF THE INVENTION

The present invention is directed to an insulating means for opticalinsulation of components which are integrated on a substrate forintegrated optics. The invention is also directed to a method for makingthe insulating means.

Integrated optical components on an InP substrate are considered costbeneficial for optical communication transmission because planartechnology replaces micro optics and micro mechanics. However, as aconsequence of integration, the interaction between the individualcomponents increases so that an undesired cross-talk arises betweenvarious transmission channels. Integration is therefore meaningful onlyto the extent to which one succeeds in realizing component structureswith a high cross-talk attenuation.

Semi-insulating substrates, separating trenches and, in addition,shielding electrodes have been used for improving the electricalcross-talk attenuation for epitaxially grown components. Measures havealso been undertaken against optical cross-talk in integrated optics.Light absorbing InGaAs layers are sometimes used for this purpose onsubstrates of InP. An example of this is disclosed in an article byBornholdt et al "WAVEGUIDE-INTEGRATED PIN PHOTODIODE ON InP",Electronics Letters, Vol. 23, No. 1, 2nd Jan. 1987, pp. 2-4. The layerof thickness needed for complete absorption cannot be realized with thestandard epitaxial method. Since the scattered light is uniformlydistributed by multiple reflections in the crystal due to a highrefractive index, individual separating trenches also seem ratherunpromising.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an insulating meanswith which integrated components can be largely decoupled from theoptical disturbances transmitted in the substrate and to a method forforming the insulating means. These objects are obtained in an improvedinsulating means for optical insulation of optical components on asubstrate for integrated optics wherein the insulating means is composedof at least two slots formed in the surface of the substrate andproceeding at a distance side-by-side along the surface, said slotsextending into the substrate obliquely in a direction towards oneanother to a depth to merge or intersect with one another so as toisolate a separate portion of the substrate or substrate region betweenthe two slots from the remainder or remaining portions of the substrate,said substrate region being connected to the remaining portion at leastat one end of the path formed by said slots.

In the insulating means of the present invention, an element, forexample a photodiode, which is integrated on the surface of thesubstrate region lying between the two slots can be better decoupledfrom the scattered light in the substrate. The substrate region ispreferably monolithically joined to the substrate at the two ends sothat contacts for active elements can also be provided on the surface ofthe substrate. Scattered light can proceed into the substrate regiononly over these end connections and can possibly pass with a lowtransmission through the slots.

The insulating means of the invention are very advantageously used insubstrates of InP.

To further reduce the slight transmission through the slots, it isexpedient that the slots be filled with a light blocking material or alight absorbing material, such as a metal or a ternary absorbingmaterial, such as InGaAs, respectively. The filling of the slots willimprove the thermic coupling and the demand for a low dissipated powerof the insulating component that otherwise exists can also beeliminated.

The insulating means of the invention is manufactured in a very simpleway by a method comprising the steps of providing a substrate having asurface, impinging two laser rays or beams that are directed onto thesubstrate's surface obliquely in a direction towards one another andimpinge on a surface limited only in a stripped-shape region thatproceeds at a distance next to one another to define slots in thesubstrate, while impinging the laser rays, laser-induced chemicallyetching the substrate in the region of the laser rays contact to a depththat occurs with the slots merging or intersecting with one another inthe interior of the substrate. Preferably, prior to impinging the laserrays or beams on the substrate, the method includes providing a shadowmask having two parallel extending slots to limit the portion of thesurface of the substrate contacted by the two laser beams. After formingthe slots, the slots may be filled with the metal or the ternaryabsorbing material or some other material after this manufacturing.Filling with metal can be carried out by a metal deposition.

Other advantages and features of the invention will be readily apparentfrom the following description of preferred embodiments, the drawingsand claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating the insulating means of thepresent invention;

FIG. 2 is a cross sectional view of the insulating means of the presentinvention, wherein the slots are filled with a metal; and

FIG. 3 is a cross sectional view similar to FIG. 2, wherein the slotsare filled with a ternary absorbing material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The principles of the present invention are particularly useful forforming an insulating means, generally indicated at J in FIGS. 2 and 3,for a substrate S. The substrate S has a surface SO and the insulatingmeans J is formed by two slots Sl₁ and Sl₂, which extend into thesubstrate S from the substrate surface SO at a spacing d therebetweenand obliquely towards one another until they intersect or merge beneaththe surface SO.

As illustrated in FIG. 1, the surface SO of the substrate S is providedwith a shadow mask Ma, which has two parallel extending slots MaS₁ andMaS₂ which have a distance d between them and a length L₁ and L₂,respectively. Thus, each of the slots Sl₁ and Sl₂ will have the lengthsL₁ and L₂, respectively, and, as illustrated in FIG. 1, the two slotsSl₁ and Sl₂ merge inside the substrate S at a point or path St whichalso will have the length L₁ and L₂.

Together, the two slots Sl₁ and Sl₂ form the insulating means J thatseparate a substrate region or portion SG, which extends between the twoslots Sl₁ and Sl₂ and which has a triangular profile from the substrateS for a defined path St and leaves a monolithic connection in thesubstrate region SG to the substrate S at least at one end e of thispath. In practice, a monolithic connection of the substrate region SG tothe substrate S will usually be left at both ends of the path St so thatthis region SG forms a bridge.

One or more passive components are integrated or can be integrated atthe surface of the substrate region SG, and the components will then beoptically insulated from the substrate. These components are, thus,optically decoupled from the remainder of the substrate S.

The manufacture of the insulating means J can occur so that the slotsSl₁ and Sl₂ are produced by a laser-induced, wet-chemical etching withtwo laser beams or light rays 2S₁ and 2S₂ which are directed onto thesubstrate surface SO obliquely in a direction toward one another. Thus,the two recesses or slots MaS₁ and MaS₂ insure that the light raysimpinge the substrate surface SO only in the regions of the recesses.The laser beams 2S₁ and 2S₂ should at least nearly extend parallel.Etching into the depth of the substrate S is carried out with theassistance of these laser beams 2S₁ and 2S₂ until the slots Sl₁ and Sl₂merge into one another or cross one another in the interior of thesubstrate S.

In the illustrated example of FIG. 1, every laser beams 2S₁ or,respectively, 2S₂ impinges on both of the recesses MaS₁ and MaS₂ so thattwo additional slots Sl₃ and Sl₄ occur in addition to the slots Sl₁ andSl₂. These additional slots Sl₃ and Sl₄ proceed into the depth from thesubstrate surface SO and diverge from one another obliquely.

Laser-induced, wet-chemical etching, for example, is known and isdisclosed in an article by Lum et al, "Improvements in the modulationamplitude of submicron gratings produced in n-InP by directphotoelectrochemical etching", Applied Physics Letter, Vol. 47, No. 3, 1Aug. 1985, pp. 269-271. Thus, since a known and conventional etchingprocess is being used, a further detailed description of the process isnot included.

In one exemplary embodiment, two substrate regions SG lying next to oneanother at a distance of approximately 200 μm were produced in then-doped InP substrate (100) surface. The slots Sl₁ and Sl₂ were etchedby a laser-induced, wet-chemical etching with two expanded nearlyplane-wave laser beams that were symmetrically incident onto thesubstrate surface SO at a 45° angle. The light wavelength of 488 nm anda light intensity of 180 mW/cm² per beam was present. A vapor-depositedtitanium film was used as a shadow mask Ma and had a pair of recessesMaS₁ and MaS₂ of a size of 3-8 μm broad that were opened by a lift-offprocess. A spacing d of the recess MaS₁ and MaS₂ amounted to 50 μm. Therecesses MaS₁ and MaS₂ and, thus, the substrate region SG as well, werelimited to a length L₁ and L₂ of 1000 μm by a local overdepositing orre-depositing of a layer of chromium. The depth of 35-40 μm required forthe slots Sl₁ and Sl₂ was achieved by using an etching solution of HCl:HNO₃ : H₂ O in a ratio of 1:1:20, respectively, for 30 minutes at 0.7volts anodic specimen potential, with reference to a calomel electrode.

For the insulation of real components, a contact metallization that isalways present can serve as the shadow mask Ma. Since a p-dopedmaterial, unlike an n-doped material, is not attacked by visible lightin the etching solution, p-doped epitaxial layers can also serve as ashadow mask Ma in the above method.

After the formation of the slots Sl₁ and Sl₂, a filling of the slotswith either a metal or a ternary absorber material can be carried out.An example of a ternary absorber material is InGaAs.

Although various minor modifications may be suggested by those versed inthe art, it should be understood that we wish to embody within the scopeof the patent granted hereon all such modifications as reasonably andproperly come within the scope of our contribution to the art.

We claim:
 1. An arrangement for optical insulation of an opticalcomponent on a substrate for integrated optical devices, saidarrangement comprising insulating means for insulating a substrateregion from a remaining portion of the substrate, said insulating meansbeing formed by at least two slots formed in the substrate and extendingobliquely in from a substrate surface to intersect each other in theinterior of the substrate to form a substrate region therebetween havinga monolithic connection to the remaining portion of the substrate atleast at one end, said substrate region having a size determined by thespacing of the slots at the surface of the substrate and a lengthdefined by the length of the two slots.
 2. An arrangement according toclaim 1, wherein the substrate is composed of InP.
 3. An arrangementaccording to claim 2, wherein at least one of the slots is filled with ametal.
 4. An arrangement according to claim 2, wherein at least one ofthe slots is provided with a ternary absorber material.
 5. Anarrangement according to claim 1, wherein at least one of the slots isfilled with a ternary absorber material.
 6. An arrangement according toclaim 1, wherein at least one of the slots is filled with a metal.